The present invention relates to a folding method for forming a sealed tubular wrapping.
In particular, the invention relates to a folding method for forming a sealed tubular wrapping about a packet of cigarettes or a group of packets of cigarettes, to which the following description refers purely by way of example. In the following description, the product for wrapping is referred to, purely for the sake of simplicity, as the "packet", with no limitation intended.
In the tobacco industry, a sheet of wrapping material is normally folded into a tube about a packet of cigarettes, or a parallelepiped group of packets of cigarettes, having four lateral surfaces. The sheet of wrapping material is folded by means of a folding device comprising a pocket conveyor, which is fed in steps along a given path along which folding means are provided. The packet is normally fed, together with the sheet of wrapping material, into a respective pocket on the conveyor to form a first U-shaped fold, and two end portions of the sheet are then folded one on top of the other to form a tubular wrapping.
In the above known method, the sheet of wrapping material is fed to the folding device with one of the end portions already coated with adhesive, so as to seal the wrapping when the two end portions are superimposed.
Though a fast way of forming sealed tubular wrappings, the above method fails to prevent the adhesive on one of the end portions of the sheet of wrapping material from fouling the components of the folding device or the packets themselves, and so impairing operation of the device and the appearance of the packet.
One proposed solution to the problem is to supply the sheet of wrapping material without the adhesive, and to apply the adhesive just before the last end portion is folded.
For example DE-C-435340 discloses a wrapping device, wherein the sheet of wrapping material is supplied without the adhesive and the adhesive is applied just before the last end portion is folded. According to DE-C-435340, a product, in particular tobacco powder, is fed in a U-shaped wrapping sheet arranged in a folding pocket with two end portions of the wrapping sheet extending outside the pocket; then a first of the end portions is partially folded over the product. To allow completing the folding of the first end portion, that is to allow further folding an end part of the first end portion over 90.degree. about the product, a portion of the wrapping sheet adjacent to a second of the end portions is slightly detached from the product. During the above detachment operation, the second end portion, which is still in its unfolded configuration, is gummed just before its folding over the first end portion.
Even this method, however, is not altogether satisfactory by prolonging stoppage of the conveyor to apply the adhesive at the station where the last end portion is folded, and on account of the difficulty, for reasons of space, in installing gumming devices immediately upstream from the station where the last end portion is folded.
Moreover, the above known method involves the additional drawback of requiring the use of a relatively complicated deformable pocket.